Method for operating a hand-held power tool, and hand-held power tool

Abstract

Method for operating a hand-held power tool, the hand-held power tool comprising an electric motor and an interface mechanically connected to the electric motor for receiving various tools, the method comprising the method steps: S1 - Starting the electric motor and driving the electric motor to a predetermined target speed; S2 - Determining a signal of an operating variable of the electric motor; S3 - Based at least in part on the operating variable signal, determining at least one characteristic of a tool connected to the interface; S4 - Controlling the handheld power tool based at least in part on the at least one feature of the tool connected to the interface.

Description

[0001] The invention relates to a method for operating a hand-held power tool, a hand-held power tool, a control unit, a computer program, and a computer-readable data carrier. State of the art

[0002] Electric hand tools with a tool holder for holding various tools are known in the art. Examples include power cutters that can accommodate a selection of different cutting, grinding, and roughing discs; impact wrenches that can accommodate a selection of tool bits of different diameters; and drills whose tool holders can accommodate various tools such as drills, metal brushes, or hole saws.

[0003] Components of a handheld power tool are subjected to varying loads depending on the tool used. For example, the load on electrical components such as MOSFETs (metal-oxide-semiconductor field-effect transistors) of a handheld power tool when the electric motor's speed changes depends on the moment of inertia of the connected tool. For example, the moment of inertia of a 3mm diameter drill bit connected to a power drill is very small compared to the moment of inertia of a 150mm diameter hole saw connected to the power drill.

[0004] To ensure safe and damage-free operation of the handheld power tool with all permissible connectable tools, certain control parameters in the control unit of the handheld power tool are, in the state of the art, adjusted to the most unfavorable characteristics of the various tools that can be used. For example, the control parameters for braking and acceleration of the speed in cut-off wheels are designed for the wheel with the greatest moment of inertia, such as a diamond grinding wheel. However, if a very thin, lightweight cutting wheel with a low moment of inertia is used as a tool, the control of the electric motor is inefficient or not optimized, for example, the wheel decelerates more slowly than actually possible. In some cases, this can lead to annoying delays in the workflow or even pose a safety risk.

[0005] Other control parameters designed for the worst case with regard to a variety of usable tools include, for example, permissible temperature limits during operation of the electric motor.

[0006] It is an object of the invention to provide an alternative or improved method for operating a hand-held power tool, as well as a control unit of a hand-held power tool, a hand-held power tool, a computer program for carrying out the method, and a computer-readable data carrier. Disclosure of the invention

[0007] The object of the invention is achieved by means of a method for operating a hand-held power tool according to claim 1, by a hand-held power tool according to claim 10, by a control unit according to claim 12, and by a computer program according to claim 13. Advantageous developments, additional features and / or advantages of the invention emerge from the dependent claims and the following description.

[0008] According to a first aspect, the present disclosure discloses a method for operating a hand-held power tool, the hand-held power tool comprising an electric motor and an interface mechanically connected to the electric motor for receiving various tools, the method comprising the method steps: S1 - Starting the electric motor and driving the electric motor to a predetermined target speed; S2 - Determining a signal of an operating variable of the electric motor; S3 - Based at least in part on the operating variable signal, determining at least one characteristic of a tool connected to the interface; S4 - Controlling the handheld power tool based at least in part on the at least one feature of the tool connected to the interface.

[0009] According to a further aspect, the present disclosure discloses a handheld power tool comprising: an electric motor; an interface mechanically connected to the electric motor for receiving various tools; suitable sensors for detecting a signal of an operating variable of the electric motor; a control unit configured to perform the following steps: S1' - after starting the electric motor, driving the electric motor to a predetermined target speed; S2 - Determining a signal of an operating variable of the electric motor; S3 - Based at least in part on the operating variable signal, determining at least one characteristic of a tool connected to the interface; S4 - Controlling the handheld power tool based at least in part on the at least one feature of the tool connected to the interface.

[0010] According to a further aspect, the present disclosure discloses a control unit for a hand-held power tool, configured to carry out the method described above.

[0011] According to a further aspect, the present disclosure discloses a computer program for carrying out the method described above when the computer program is executed by a control unit of a hand-held power tool or is stored on a computer-readable data carrier.

[0012] According to a further aspect, the present disclosure discloses a computer-readable data carrier on which a computer program as described above is stored.

[0013] Step S2 may be executed while the electric motor is driven to the predetermined target speed in step S1.

[0014] The operating variable can be a motor current or an operating variable correlated with the motor current.

[0015] The operating variable can be a speed of the electric motor or an operating variable correlated with the speed.

[0016] The signal of the operating variable can be recorded in process step S2 as a time course of measured values ​​of the operating variable.

[0017] The at least one feature in steps S3 and S4 may be a mass moment of inertia of the tool.

[0018] The at least one feature in steps S3 and S4 may be a purpose of the tool.

[0019] In step S4, speed changes of the electric motor during operation of the handheld power tool can be controlled at least partially based on the at least one feature of the tool connected to the interface.

[0020] In step S4, allowable maximum and / or minimum temperature limits of the electric motor may be set based at least in part on the at least one feature of the tool connected to the interface.

[0021] The hand tool can be a hand tool from the group comprising a cutting machine, milling machine, router, impact wrench, screwdriver, drill, and impact drill. Short description of the characters

[0022] The invention is explained in more detail below using exemplary embodiments with reference to the attached schematic drawings, which are not to scale. The figures (Fig.) of the drawings, which are merely exemplary, show: Fig. 1 a schematic representation of an electric hand tool; Fig. 2 schematically shows an embodiment of a method for operating a hand-held power tool, as well as a hand-held power tool; Fig. 3 schematically shows two signals of an operating variable; Fig. 4 shows an embodiment of a tool used with a hand-held power tool; Fig. 5 of a sectional view of an embodiment of a tool used with a hand-held power tool.

[0023] Based on the Fig. 1 to 5, the method for operating a hand-held power tool and a hand-held power tool are described schematically below.

[0024] The Fig. 1 shows a handheld power tool 100 having a housing 105 with a handle 115. According to the illustrated embodiment, the handheld power tool 100 is mechanically and electrically connectable to a battery pack 190 for mains-independent power supply. Fig. 1, the handheld power tool 100 is embodied, for example, as a cordless impact wrench. However, the present invention is not limited to cordless impact wrenches, but can in principle be used with any handheld power tool 100 that has an electric motor and a tool holder for holding various tools. Examples include cut-off machines, milling machines, routers, impact wrenches, screwdrivers, drills, and hammer drills.

[0025] An electric motor 180, powered by the battery pack 190, and a gear 170 are arranged in the housing 105. The electric motor 180 is connected to an input spindle via the gear 170. Furthermore, a control unit 370 is arranged within the housing 105 in the area of ​​the battery pack 190. This control unit 370 acts on the electric motor 180 and the gear 170 for controlling and / or regulating them, for example, by means of a set motor speed n, a selected angular momentum, a desired gear x, or the like.

[0026] The electric motor 180 can be operated, for example, via a manual switch 195, i.e., switched on and off, and can be any type of electric motor, such as an electronically commutated motor or a DC motor. In principle, the electric motor 180 can be electronically controlled or regulated in such a way that both reversing operation and specifications regarding the desired motor speed n and the desired angular momentum can be implemented. The operation and design of a suitable electric motor are well known in the art.

[0027] A tool holder 140 is rotatably mounted in the housing 105 via an input spindle and an output spindle 150. The tool holder 140 serves to hold a tool and can be molded directly onto the output spindle 150 or connected to it in the form of an attachment. As already mentioned above, the tools that can be accommodated can vary greatly with regard to certain characteristics, such as their moment of inertia. This is generally desirable in order to ensure that the handheld power tool 100 is suitable for machining the widest possible range of workpieces.

[0028] The control unit 370 is connected to a power source and is configured to electronically control and regulate the electric motor 180 using various current signals. The various current signals provide different rotational impulses for the electric motor 180, with the current signals being transmitted to the electric motor 180 via a control line. The power source can be configured, for example, as a battery or, as in the illustrated embodiment, as a rechargeable battery pack 190 or as a mains connection.

[0029] Furthermore, control elements not shown in detail may be provided to set different operating modes and / or the direction of rotation of the electric motor 180.

[0030] In Fig. 2, the hand-held power tool 100 is designed as a cut-off grinder. As indicated, the hand-held power tool 100 can be used with various discs as tools, for example, with a cutting disc 201 and a diamond cup wheel 202 for surface treatment of concrete. The person skilled in the art knows that cutting discs 201 have a relatively small thickness (perpendicular to the plane of the drawing in Fig. 2), whereas diamond cup wheels 202 have a larger one in order to withstand stresses perpendicular to the plane of the wheel which may occur during normal use.

[0031] Due to its low mass and the resulting small moment of inertia, the cutting disc 201 could be driven by the electric motor of the hand-held power tool 100 (in Fig. 2 not shown) can be accelerated and braked relatively quickly, which would be advantageous and desirable in the operation of the hand-held power tool 100, since the shorter braking time results in advantages with regard to user safety, for example.

[0032] However, the diamond cup wheel 202, which can also be used with the hand tool 100, has a significantly larger mass moment of inertia, and if the control unit (in Fig. If the control system (not shown in Figure 2) were to control the electric motor with control parameters optimized for the cutting wheel 201, this could result in mechanical, electrical, and / or thermal overloading of certain components of the handheld power tool 100. In this context, reference was made above, for example, to the stress on electrical components such as MOSFETs, which varies depending on the mass moment of inertia of the connected tools. Another example is the temperature load on certain electrical components, which must be within limits specified and monitored by the control device.

[0033] In the state of the art, the control unit of the hand-held power tool is therefore set up for the worst case, and in Fig. In the case illustrated in Figure 2, a known control unit would therefore control both the cutting wheel 201 and the diamond cup wheel 202 with the same control parameters, which, however, would be optimized for the diamond cup wheel 202 for the reasons mentioned. In this case, the cutting wheel 201 would, for example, be decelerated unnecessarily slowly.

[0034] The method disclosed below for operating the handheld power tool 100 allows, in contrast to the aforementioned prior art, the handheld power tool 100 to be operated with different tools under optimized control parameters, largely independent of whether it is operated, for example, together with the cutting wheel 201 or with the diamond cup wheel 202. For this purpose, at least one feature of the tool used is automatically recognized by the control unit without user input being required and without the need for an enlarged sensor system compared to known, corresponding handheld power tools 100.

[0035] According to the method, the electric motor 180 is started in a step S1. In the hand-held power tool 100, this is usually done by a user who presses a switch such as the one shown in Fig. 1 is actuated. In response, the control unit drives the electric motor 180 to a predetermined target speed, which varies depending on the handheld power tool 100.

[0036] In a simplified representation, the speed of the electric motor 180 undergoes a ramp from zero to the predetermined target speed. In a step S2, which occurs essentially parallel to the ramp-up of the speed of the electric motor 180, a signal of an operating variable of the electric motor is determined and stored. In embodiments, the signal, the operating variable, is a curve of the motor current over time, as shown in Fig. 3 is shown schematically. In the Fig. In the diagram shown in Figure 3, time t is plotted on the ordinate and motor current I on the abscissa. The diagram shows two signals 501, 502 of the motor current. Those skilled in the art will recognize that both the first signal 501 and the second signal 502 represent a motor current profile that is established as a result of adjusting a predetermined speed characteristic. In the figure, the motor current follows a linear ramp from zero to a specific value, which is indicated by the plateau 600. In the diagram shown in Fig. 3, the plateau 600 has a higher value of the motor current for the signal 501 than for the signal 502. In Fig. 3, the signal 502 represents the course of the motor current when the hand-held power tool 100 is operated with the cutting wheel 201, and the signal 501 represents the course of the motor current when the hand-held power tool 100 is operated with the diamond cup wheel 202.

[0037] In a step S3, at least one feature of the tool connected to the interface is determined, at least in part, based on the operating variable signal. Fig. In the example shown in Figure 2, this feature is the moment of inertia of the cutting wheel 201 or the diamond cup wheel 202, or an order of magnitude thereof.

[0038] The method according to the invention makes use of the fact that certain signals of operating variables, for example the Fig. 3, the motor current curve can have different curves when using different tools. Fig. 3, for example, it can be seen that the signal 501 in the range between I=0 and the plateau 600 has a steeper curve than the signal 502, whereby the different gradients in Fig. 3 are indicated by the angles α1 and α2. This is due to the fact that the speed change of the diamond cup wheel 202 after the motor has started up occurs more slowly than with the cutting wheel 201, since the diamond cup wheel 202 has a greater moment of inertia. With the starting characteristics set in the control unit, the electric motor requires more current to effect the specified speed changes of the diamond cup wheel 202, and accordingly, the motor current, which correlates with the speed, increases more quickly than is the case when operating with the cutting wheel 201. Based on the gradients α1, α2, conclusions can be drawn about the "moment of inertia" characteristic of the tool used, and if necessary, based on this, also about the intended use or the type of tool (e.g., light cutting wheel or heavy grinding wheel).

[0039] To rotate the diamond cup wheel 202, an overall higher motor current is also required, which is why the signal 501 in the region of the plateau 600 is also at a higher level than the signal 502. This aspect can also be used in step S3 to determine one or more features of the tool connected to the interface.

[0040] In embodiments of the invention, corresponding relationships between the course of the operating variable signal—in the example, various gradients and plateaus of the motor current—and tool types or their characteristics, such as mass moments of inertia, are stored in software in the control unit of handheld power tool 100. These relationships are then accessed in step S3 after the operating variable signal has been determined.

[0041] Using the motor current curve as a signal of the operating variable is advantageous because the motor current in known handheld power tools 100 is already detected by the control unit, thus eliminating the need for additional sensors. The motor current signal can be determined, for example, in a conventional manner using a shunt resistor, which first determines the motor voltage, which is then used to determine the motor current.

[0042] The signal of the operating variable can be recorded quasi-continuously as a time course of measured values ​​of the operating variable. Fig. The curve of the signals 501, 502 shown in Figure 3 is simplified and idealized, and other curves are conceivable, depending on the characteristics of the speed curve specified by the control unit.

[0043] In a step S4, the hand-held power tool 100 is now controlled at least partially based on the at least one feature of the tool connected to the interface, for example by setting certain parameters depending on the detected feature. For example, in the Fig. 2, it is detected on the basis of the signal 502 of the motor current or on the basis of the relatively small gradient α2 thereof when starting up the motor that a disk with a relatively small mass moment of inertia is being used with the hand-held power tool, a control parameter which regulates the fastest permissible braking or the fastest permissible acceleration of the speed of the tool can be set to a specific value which is different from the value which would be set if it were detected on the basis of the signal 501 of the motor current that a disk with a relatively large mass moment of inertia is being used.

[0044] In embodiments of the method, the operating variable signal determined in step S2 can also be a curve of a torque applied to the output spindle of the electric motor of the handheld power tool 100, which is transmitted from the output spindle to the tool. The magnitude of the torque can be determined, for example, via sensors arranged on the output spindle, which measure a torsion of the output spindle, which is then converted into a corresponding torque. Similar to the Fig. In the embodiment shown in Figure 3, the moment of inertia of the tool used can be determined from the growth rate of the torque.

[0045] In a further embodiment, the handheld power tool 100 is a milling machine, in particular a router. Such milling machines can be operated with various rotationally driven, substantially circular or cylindrical milling tools for machining wood, for example. A typical milling tool 205 is shown in Fig. 4 is shown schematically. It has a shank section 206 which is identical for all tools and is clamped into a tool holder of the router, and a cutting edge 207 arranged on a periphery of the milling tool 205 with a radius r and spaced from a rotation axis x. Milling tools 205 with different radii r are typically used when machining a workpiece. The cutting edge 207 should advantageously have the same peripheral speed across different milling tools 205, which is selected, for example, depending on the material to be machined. Since the peripheral speed of the cutting edge is linearly dependent on the radius r of the milling tool 205, a milling tool 205 with a larger radius r must be operated at a lower speed than a milling tool with a smaller radius r for a given peripheral speed.

[0046] The Fig. 2 and Fig. The method according to the invention described in Figure 3 can be used to determine at least an order of magnitude of the radius r of the milling tool 205 used with the milling machine and to set a rotational speed of the electric motor as a control parameter such that the cutting edge 207 is moved at the desired path speed.

[0047] For this purpose, as described above, a mass moment of inertia of the milling tool 205 is determined, or at least an order of magnitude thereof, based on a signal of an operating variable, for example the motor current or the torque. From the mass moment of inertia, in step S3, using the known relationship J=12mr2 The radius r can be determined from the relationship between the radius r of a circular disk, its mass m, and its moment of inertia J, taking into account that the milling tools used have a similar mass, at least in terms of magnitude, and the moment of inertia is therefore primarily determined by the influence of the radius r, which is quadratically included in equation (1). In step S4, a control parameter can then be set that controls the rotational speed of the electric motor such that the desired path speed of the cutting edge 207 is established.

[0048] In a further embodiment, which is described below with reference to Fig. 5, the hand tool 100 is a rotary impact wrench, as in Fig. 1. Together with the impact wrench, a tool bit 210 is used to grip hexagon heads 215 of fasteners 214, which is connected to the tool holder 140 via an adapter 212. Depending on the wrench size of the hexagon head 215 of the fastener 214, the tool bit 210 also has different dimensions, which can be approximately represented by a circumferential radius r of the hexagon head 215. A rotation axis is shown in the sectional view of Fig. 5 marked with x.

[0049] A "free socket mode" can be used to release a tool bit 210 that is jammed with the hexagon head 215 while screwing the fastener 214 into or out of a screw base 216 by applying a short rotary impulse in the direction of rotation opposite to the respective direction of rotation of the screwing process. This rotary impulse can vary in size depending on the holding force of the fastener 214. If the fastener 214 has a relatively small diameter, which means that it also has a relatively small hexagon head 215, its holding force is generally also relatively small, and the rotary impulse in free socket mode should be selected accordingly. Conversely, a larger rotary impulse can be selected if the fastener 214 has a relatively large diameter, and thus a relatively large hexagon head 215.

[0050] The method according to the invention described above can be used to determine at least the order of magnitude of the circumferential radius r and, depending thereon, to set a level of the angular momentum of the free socket mode as a control parameter.

[0051] For this purpose, as described above, a mass moment of inertia of the tool bit 210 is determined based on a signal of an operating variable, for example the motor current or the torque. From the mass moment of inertia, an order of magnitude of the circumferential radius r of the tool bit 210 can be deduced in step S3 as described above via the relationship known from equation (1), again taking into account the fact that the mass moment of inertia is primarily determined by the influence of the circumferential radius r which is quadratically included in equation (1). The calculation presented here does not take into account geometric peculiarities of the Fig. 5 such as the partial hollowing of the tool body in the area of ​​the opening for receiving the hexagon head 215, as well as the fact that the circumferential radius r is as in Fig. 5 is clearly an inner radius of the tool bit 210, while the radius used in equation (1) is an outer radius. Appropriate adjustments and refinements of the calculation approach can be made in equation (1) without fundamentally changing the solution method.

[0052] If, as indicated, the diameter of the tool bit 210 or its order of magnitude has been determined, the diameter of the fastening means 214 or its order of magnitude is also known, and a permitted or required magnitude of the angular momentum can be determined at least partially on this basis, for example by experimentally determined relationships between the diameter of the fastening means 214 and corresponding angular momentums in free socket mode that are stored in the software in the control unit.

[0053] In step S4, a control parameter can then be set that controls the size of the angular momentum used in free socket mode.

[0054] The invention is not limited to the described and illustrated embodiments. Rather, it also encompasses all developments within the scope of the invention defined by the patent claims. In addition to the described and illustrated embodiments, further embodiments are conceivable, which may include further modifications and combinations of features.

Claims

[1] Method for operating a hand-held power tool, the hand-held power tool comprising an electric motor and an interface mechanically connected to the electric motor for receiving various tools, the method comprising the method steps: S1 - Starting the electric motor and driving the electric motor to a predetermined target speed; S2 - Determining a signal of an operating variable of the electric motor; S3 - Based at least in part on the operating variable signal, determining at least one characteristic of a tool connected to the interface; S4 - Controlling the handheld power tool based at least in part on the at least one feature of the tool connected to the interface. [2] Method according to claim 1, characterized by that step S2 is carried out while the electric motor is driven to the predetermined target speed in step S1. [3] Method according to one of claims 1 and 2, characterized by that the operating variable is a motor current or an operating variable correlated with the motor current. [4] Method according to one of claims 1 to 3, characterized by that the operating variable is a speed of the electric motor or an operating variable correlated with the speed. [5] Method according to one of claims 1 to 3, characterized by that the signal of the operating variable is recorded in process step S2 as a time course of measured values ​​of the operating variable. [6] Method according to one of claims 1 to 4, characterized by that the at least one feature in steps S3 and S4 is a mass moment of inertia of the tool. [7] Method according to one of claims 1 to 5, characterized by that the at least one feature in steps S3 and S4 is a purpose of the tool. [8] Method according to one of claims 1 to 6, characterized bythat in step S4, speed changes of the electric motor during operation of the hand-held power tool are controlled at least partially on the basis of the at least one feature of the tool connected to the interface. [9] Method according to one of claims 1 to 6, characterized by that in step S4, permissible maximum and / or minimum temperature limits of the electric motor are set at least partially based on the at least one feature of the tool connected to the interface. [10] Hand tool, comprising: an electric motor; an interface mechanically connected to the electric motor for holding various tools; suitable sensors for detecting a signal of an operating variable of the electric motor; a control unit configured to perform the following steps: S1' - after starting the electric motor, driving the electric motor to a predetermined target speed; S2 - Determining a signal of an operating variable of the electric motor; S3 - Based at least in part on the operating variable signal, determining at least one characteristic of a tool connected to the interface; S4 - Controlling the handheld power tool based at least in part on the at least one feature of the tool connected to the interface. [11] Hand tool according to claim 9, characterized by that the hand-held power tool is a hand-held power tool from the group comprising cut-off grinders, milling machines, routers, impact wrenches, screwdrivers, drills and impact drills. [12] Control unit for a hand-held power tool, configured to carry out the method according to one of claims 1 to 8. [13] Computer program for carrying out the method according to one of claims 1 to 8, if the computer program is executed by a control unit of a hand-held power tool or is stored on a computer-readable data carrier. [14] A computer-readable data carrier on which a computer program according to claim 12 is stored.

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